The composition of the metal melt plays an important role in the production of high-quality aluminum castings. A melt with high hydrogen content often leads to defects and macro porosity [1]. Gas purging treatment and the use of melting salts for degassing are commonly used to reduce the hydrogen content. However, a consistent solidification of the entire cast part cannot always be realized. In these cases, undesired macro porosity may occur due to hydrogen excess in comparison to the amount of porous seeds in the melt. 

In recent years, the Institute of Nonferrous Metallurgy and Purest Materials has identified two ways of positively influencing this hydrogen porosity. On the one hand, it was found out that it is possible to use a special melt additive to adjust the ratio between the hydrogen dissolved in the melt and the existing pore nuclei so that the hydrogen released during solidification is finely distributed in the casting [2]. On the other hand, it was shown that the use of reactive filter materials can positively influence the precipitation of the atomically dissolved hydrogen and thus generate denser castings [3,4]. Both processes are presented and the efficiency and influence of the respective filter materials and additives is explained. 

The metallurgical industry is continuously seeking sustainable methods for the valorization of materials, such as tin residues, which arise as a byproduct during production processes for example in soldering printed circuit boards. This study focuses on the utilization of green, non-fossil reducing agents, specifically biomasses, for the recovery of tin from industrial residues. These can contain valuable amounts of tin and other valuable metals (e.g. Ag and Cu) that can be recovered and reused, essentially making its valorization not only environmentally imperative, but also economically beneficial. When treated correctly the produced secondary slag can become a valuable base product for cement production. This study aims to prove exemplary pathways for holistic valorization of two distinct tin residues.

Biomasses, abundant and renewable, from agricultural, forestry and other organic sources, are considered carbon-neutral due to the fact that they absorb as much carbon during their “life”, as they release when utilized. This more climate friendly status holds especially true for low-grade byproducts. In pyrometallurgy, the use of biomasses as reducing agents is a rapidly growing field of research, providing greener alternatives to the traditional reducing agents such as coke [1][2][3]. This work, is also aimed to explore the effectiveness of different biomasses in the reduction of tin oxides from the residues to their metallic form [4]. 

With regard to the experimental procedure, various biomass types such as straw, wood, coconut shells etc. were used [5] and compared against traditional coke. The reduction process was carried out in crucible experiments under inert gas in completely molten systems, while optimizing the parameters of temperature, reaction time and tin residue / biomass ratio as well as fluxing, in order to minimize the concentration of impurities in the metallic phases. 

For some residues a prior leaching step is explored and compared against direct pyrometallurgical treatment. Neutral and acidic leaching was investigated with the purpose of decreasing Cl and S amounts which are potentially undesired in the following pyrometallurgical step.

In conclusion, the study demonstrates the feasibility of using biomass reducing agents as greener reducing agents for the valorization of tin residues. The approach aligns with the principles of circular economy and offers a pathway towards more sustainable metallurgical processes. The successful recovery of tin using biomasses could lead to a reduction in the industry’s carbon footprint and contribute to the conservation of natural resources.